1. Field of the invention
The present invention relates to an acryl-based pressure-sensitive adhesive composition. More particularly, the present invention relates to an antistatic pressure-sensitive adhesive composition, and pressure-sensitive adhesive sheets using the same. In particular, pressure-sensitive adhesive sheets of the present invention are useful as a surface protecting film (a protecting film) used for the purpose of protecting a surface of an optical member such as a polarizing plate, a wavelength plate, a phase difference plate, an optical compensating film, a reflecting sheet, and a luminance improving film which are used as a liquid crystal display or the like.
2. Description of the Related Art
A pressure-sensitive adhesive sheet can be adhered by applying a slight pressure at a normal temperature for a short time, and is used in various utilities for connecting various articles. In addition, since a pressure-sensitive adhesive sheet has a cohesive strength and elasticity, the sheet is suitably adhered and, conversely, can be peeled from a hard smooth surface, and is also utilized as a surface protecting film.
A surface protecting film is generally used for the purpose of preventing a scratch or a stain produced at procession or conveyance of a subject to be protected by applying to a subject to be protected via a pressure-sensitive adhesive layer coated on a protecting film side. For example, for the purpose of preventing a scratch or a stain, a surface protecting film is applied to an optical member such as a polarizing plate and a wavelength plate used in a panel of a liquid crystal display via a pressure-sensitive adhesive layer. In these optical films used for optical members, a separator is generally used for protecting the surface of a pressure-sensitive adhesive layer. In addition, in a step of applying a surface protecting film used for the purpose of protecting these optical members to optical members, since a separator become unnecessary, they are peeled and removed from an optical film.
In general, since a surface protecting film, a pressure-sensitive adhesive, and a separator which constitute a surface protecting film are constructed of a plastic material, they have high electric insulating property, and static electricity is generated upon friction or peeling. Therefore, there is a problem that, also upon peeling of a protecting film from an optical member such as a polarizing plate, static electricity is generated. Due to this static electricity, there arises a problem that a dust is attached to a surface protecting film or an optical member, and this pollutes an optical member. Then, in order to prevent such the disadvantage, a surface protecting film is subjected to various antistatic treatments.
Previously, as an attempt to suppress the aforementioned static electricity, for example, a method of preventing electrification by adding a low-molecular surfactant to a pressure-sensitive adhesive, and transferring a surfactant from a pressure-sensitive adhesive to an adherend has been disclosed (for example, see Patent Publication 1). However, the low-molecular surfactant is easily bled on a surface of a pressure-sensitive adhesive layer and, when applied to a surface protecting film, staining of an adherend (subject to be protected) is feared. Therefore, when a pressure-sensitive adhesive with a low-molecular surfactant added thereto is applied to a surface protecting film for an optical member, there is a problem that optical property of an optical member is deteriorated.
In addition, pressure-sensitive adhesive sheets in which an antistatic agent is contained in a pressure-sensitive adhesive layer (e.g. see Patent Reference 2) are disclosed. In such pressure-sensitive adhesive sheets, in order to suppress an antistatic agent from bleeding on a pressure-sensitive adhesive surface, an antistatic agent comprising a polyether polyol compound and an alkali metal salt is added to an acryl-based pressure-sensitive adhesive. However, even by using such pressure-sensitive adhesive sheets, phenomenon of bleeding of an antistatic agent is not avoided and, as a result, there is a problem that, in the case where actually applied to a surface protecting film, when treatment with time or under high temperature condition is performed, phenomenon is generated in which a surface protecting film is partially peeled off from a subject to be protected due to bleeding phenomenon.
As described above, in any of these, the aforementioned problems can not be solved well-balanced yet and, in the technical field associated with electronic appliances where electrification or staining becomes a particularly serious problem, it is difficult to correspond to demand of further improvement of an antistatic surface protecting film.
[Patent Publication 1] JP-A No. 9-165460
[Patent Publication 2] JP-A No. 6-128539